The Killer Rabbit of Caerbannog is a fictional beast in the movie Monty Python and the Holy Grail. It is the antagonist in a major setpiece battle, and makes a similar appearance in Spamalot, a musical inspired by the movie. The iconic status of this skit was important in establishing the viability of the musical.

In the film, King Arthur's Knights of the Round Table are led to the Cave of Caerbannog by Tim the Enchanter, and find that they must face down both the Rabbit and the Black Beast. The Cave of Caerbannog ("caer bannog" being Welsh for "turreted castle") is the home of the Legendary Black Beast of Aaaaarrrrrggggghhhhh. This is guarded by a monster which is initially unknown. King Arthur and his knights are led to the cave by Tim the Enchanter, and find that they must face down its guardian beast. Tim verbally paints a picture of a terrible monster with "nasty, big, pointy teeth!", so terrifying that Sir Robin soils his armour. When the guardian appears to be an innocuous white rabbit, surrounded by the bones of the fallen, Arthur and his knights no longer take it seriously. Ignoring Tim's warnings ("a vicious streak a mile wide!"), King Arthur orders Bors to chop its head off. Bors confidently approaches it, sword drawn, and is immediately decapitated by the rabbit to the sound of a can opener. Despite their initial shock, Sir Robin soiling his armor (again), and Tim's loud scoffing, the knights attack in force, but are driven to "run away!" as the rabbit leaps and attacks, killing Gawain and Ector. The Holy Hand Grenade of Antioch is then used to kill the beast and allow the quest to proceed.

The rabbit scene was shot outside the Tomnadashan Mine cave overlooking the Perthshire village of Killin. For the 25th anniversary DVD, Michael Palin and Terry Jones returned to be interviewed in front of the cave but they could not remember the location. They wandered up and down the hills for hours and, in desperation, asked the locals, saying that they couldn't miss it as it had a killer rabbit in it. This prompt was insufficient and so the couple performed a comic turn in front of the nearby loch to general amusement: "It was priceless stuff, and some of the looks they were getting were unbelievable."

The rabbit was portrayed in the movie by a real rabbit and also a prop. The woman who owned the real rabbit was unhappy with the amount of Kensington Gore in which it had been doused by the Python crew.